Small fix to image viewer example
Small fix to image viewer example

hawkchch/walk,CodyGuo/walk,antonlahti/go-winapi,tajtiattila/walk,ssoor/winapi,Skarm/walk,Skarm/walk,jtwatson/walk,JSchwehn/walk,dayed/walk,henrylee2cn/walk,jtwatson/win,CodyGuo/win